DiLouie: Looking at LED sources and controls, what are the different technological methods used to produce tunable-white light in commercial luminaires?

Ciccarelli: The goal of Tunable White lighting is to reproduce multiple color temperatures from a source and to allow selection or programming of the fades from one color to another. Additionally, intensity dimming (intensity fading) is also an important component of lighting design when Tunable White is employed—so fades in both color temperature and intensity are used by the designer to set the proper effect.

Here is a figure showing the CIE color space with the Black Body Locus (BBL) where white light is defined at the convergence of the three primary colors: red, green and blue. Color Temperature uses units of Kelvin, abbreviated as K (e.g., Halogen lamps typically have a Color Temperature of 3000K).

First, we will look at moving from one color to another.

Unfortunately, the area of the color space defining white light is not linear, so moving from one color temperature to another is not as straight forward as you’d think. The so-called Black Body Locus (BBL) where color temperatures are defined is a curve, and the curve gets steeper toward warmer colors (moving downwards as you move warmer). When on the Black Body Locus, the tint is neutral, and this is the target of mostly all lighting manufacturers right now for their regular static white luminaires. Once you move off the BBL, the tint will be green if above, and pink if below.

A few methods for creating Tunable White Light:

A) Warm-Cool Gamut

Warm-Cool is the method to use two different color temperature white LEDs and move on the path between them. This path is a straight line and falls off the BBL at the center. The wider the range of CCT, the further off the BBL the line will become.

But if the tunable range is narrow, this is a good approximation of the BBL and can be good enough for many applications. Care should be taken when mixing these sources with static as the colors may not match in the middle points.

This method could be extended to Warm-Netural-Cool making a segmented line, better approximating the BBL curve.

Note that limitations in availability of the extreme color temperatures becomes a disadvantage for this method to reach ultra-warm color temperatures or maintain good color rendering in the cool section.

B) Area/Triangular Gamut

The Area/Triangular Method uses different color LEDs to create a triangular zone within which the source can be tuned. Since the source can move anywhere within the zone, we can move between colors along a curve—that allows travel along the curve of the BBL.

The area can be made up of three or more colors, and the benefit of additional colors is the ability to fill out the spectral content of the light leading to better color rendering metrics—better matching natural and traditional light sources.

Further, this method has the benefit of being able to reach ultra warm color temperatures and maintain excellent color rendering metrics along the tunable range. Also, since any color within the gamut is possible, custom tunable white paths with various levels of greenish/pinkish tint (i.e. Duv) can be programmed.

Second, we look at the controls for Tunable White control systems.

Control systems for mainstream lighting have focused on energy savings and code compliance—to deliver the lighting we need for the task and provide advanced sensors and automation to save energy. These systems manage turning the lights on and off, but also have expanded to control the intensity dimming—all of these with a single handle of control: intensity. The use of intensity dimming (or intensity fading) can provide energy savings, but it can also provide aesthetic design to spaces. So, modern mainstream controls are capable of on/off/dim control of the luminaires within the system—but what about color control? Color control, in this case Color Temperature control, is not built into the modern lighting control systems—another handle of control for CCT is required.

We have two choices to bring Tunable White to the mainstream from a controls perspective:

1) We can use on/off/dimming systems and repurpose an intensity channel to deliver control of Color Temperature (or other color attributes).

2) We can design control systems that are Color Aware by including color attributes (e.g. CCT, Duv, Hue) in addition to on/off/dim.

Both of these approaches have their challenges and, if done incorrectly, can result in a poor experience for the designers/programmers, or worse they could result in the inability to accomplish the goals of the designers all together.

The first Tunable White systems in the mainstream will use (1) above. This approach will have a few limitations in that the interface/programming tools available to the designer will be left over from on/off/dim paradigm. For example, in an on/off/dim system there was not a need for long theatrical-class intensity fades over very long periods of time. So when using this system to control color temperature, you will have challenges to find a built-in function to perform a multi-hour fade. One hallmark of a Tunable White application is very long imperceptible “circadian” fades of color temperature. Adding these style fades to a system optimized for on/off/dim will be cumbersome, if not impossible. These systems will therefore not cover circadian-style applications and will be more focused on user selected scenes on demand.

Over time mainstream systems will become Color Aware, meaning the controller, network and luminaires will all be speaking to each other in handles representing color. Therefore, the user interfaces will present the user with the appropriate controls and selectors—allowing proper programming (i.e. authoring) of the space to the intended application. These systems will take into account “circadian” fades for both intensity and various color attributes—they will be purpose built for Tunable White and other advanced mainstream dynamic applications.

DiLouie: What are the different effects that can be created, such as color stability/consistency, dim-to-warm, CCT selection?

Ciccarelli: Exceptional color consistency and stability are a given for Tunable White and indeed any dynamic lighting used in the mainstream. The static white world using LEDs has already moved to a tighter consistency than the traditional sources before them, and that expectation and more is heaped upon the creators of Tunable White systems.

In our quest to bring dynamic lighting to the mainstream, we researched how designers wanted to transform their spaces, how space owners wanted to transition their space, how users of the spaces wanted to interact or be guided by their lighting, and finally how the researchers were determining links between health and lighting. What was immediately clear was that we were not using the same terminology and there was a lack of good descriptions for explaining the functions and elements of dynamic lighting.

Therefore, it is useful to define what Dynamic Features a system can perform, we’ve settled on six:

These are generic terms and are intended to be portable in our conversations with designers, manufacturers and end users. Clearly there is much more to dynamic lighting in the mainstream than just Tunable White.

Dynamic Effects would be the implementation of these features across nodes over time. Some examples would be cross fades (color or intensity), sweeps, gradients, etc. These are important as we start to discuss how people want to author the shows displayed in mainstream spaces. Dynamic Effects are out of scope for this discussion.

DiLouie: What benefits do these effects offer to various applications?

Ciccarelli: First and foremost, bringing dynamic lighting to the mainstream will result in aesthetic design elements we weren’t able to achieve previously. This means mood setting, focusing on visual interests and tapping into our natural need for daily rhythms in lighting. All this can be accomplished with subtle color and intensity fades and layering these fades across the space in different lighting forms and locations.

As research advances, we’ll move from aesthetic elements to actual support of health and well-being using light. This is why we pulled out and defined Optimized Spectrum (#6 in Q. 2) as an important feature that will let us shape the spectral content of light far beyond only adjusting Color Temperature and hue.

DiLouie: What markets and applications do different tunable-white lighting effects serve? What’s the low-hanging fruit?

Ciccarelli: Tunable White will find applications most readily in retail and hospitality–in the places where lighting helps to sell goods and services. This can be done by helping to fine tune the presentation of products for maximum visual representation, or it can mean setting and transitioning the atmosphere of a gathering space to accomplish the goals of the designers and owners.

Education and commercial office will also quickly see the benefits of Tunable White in that the links between various daily activities to color temperature is easy to make without further research. Simple systems allowing adjustment of color temperature depending on the task being performed will become as commonplace as how we control dimming now.

DiLouie: What new applications are being created by the availability of this technology?

Ciccarelli: One of the most exciting applications of Tunable White lighting is the ability to transform a space from one use to another just by adjusting the lighting. A related example from the past is how dimming was used to transform restaurants from the different atmospheres of lunch and dinner. Imagine extending that idea and having a company reception area transform from corporate identity and efficiency into evening cocktail and feature space.

But most importantly we’ll see our existing spaces where we work and live transform into more productive and comfortable environments that seamlessly change over the course of the day to match our activities.

DiLouie: How would you characterize demand for tunable-white lighting?

Ciccarelli: Interest in bringing dynamic lighting into the mainstream, starting with Tunable White, is amazing right now. We are finally at the point where the applications are understood well enough and the technology is accessible enough to make the 15-year-old dream finally come to fruition.

DiLouie: Are there any pitfalls or areas where further development and improvement is needed?

Ciccarelli: Just like the introduction of CFLs and LEDs themselves, there is always the danger that the first mass-produced Tunable White systems will be of lower quality than is necessary for true adoption. Key things to look for here are the quality of the color path the Tunable White luminaires can transition over (does it follow the BBL?), the ease of authoring the transitions (how do I make it move from 3250K at 70% to 2900K at 80%?), and how the user interface is presented to the designer and occupants of the space (does the user get direct CCT control, presets, or does it happen automatically?).

DiLouie: Color temperature has been linked to circadian lighting. What is the link, what research supports it, and how should distributors be selling it?

Ciccarelli: People learning about Tunable White are excited by the idea of the links to the human circadian system, and how we’ll start to truly affect health and well being. In almost every conversation I have on Tunable White, the word “circadian” is mentioned.

Natural light during different parts of the day can have very different influences over our circadian system. To simplify, the spectral content of the light along with how much and how long you are exposed make up the calculation on how much circadian stimulation you receive.

With LED based Tunable White lighting, we will be able to replicate the natural rhythms of the day in color temperature and intensity. This will provide people in the space with the visual comfort in a way much more natural than what traditional electric lighting systems could provide. It is important to note that LED based lighting has a different spectral makeup than natural light and therefore will have different effect on human circadian systems.

As research advances, we’ll improve the control of the spectral content of the light sources to start to achieve true circadian system impact tailored to the individuals in the space. We are reserving the dynamic feature of Optimized Spectrum for this use, along with advanced controls linked to individual’s lighting needs through Internet of Things to create just the right personal recipe.

DiLouie: What lighting controls enable tunable-white lighting? Are these typically packaged with the luminaires or paired by control manufacturers?

Ciccarelli: For dynamic lighting in the mainstream, the system is made up of three elements: Controls, Network, and Luminaires.

These three system elements must be designed to work together for dynamic lighting—they must speak the same language in order to assure consistency and accuracy. Anyone who has tried to mix Tunable White luminaires from different manufacturers together with a third-party controller knows the pitfalls as there are no standards they were all designed to meet.

Tunable White, as well as other mainstream dynamic lighting systems, must be sold as a system. The luminaires must be paired and designed with the controller and network.

DiLouie: If you could tell the entire electrical industry just one thing about LED tunable-white lighting, what would it be?

Ciccarelli: Tunable White is just one feature of dynamic lighting coming to the mainstream, look for lighting systems to expand to become Color Aware and allow transformation of spaces into living environments.